The kinetics of parasite-specific antibody responses in relation to worm burden and egg output were investigated in hamsters infected with 25, 50 and 100 Opisthorchis viverrini metacercariae (MC). Levels of antibody to egg, excretory-secretory (ES) and somatic antigens were examined by ELISA on days 1, 3, 7, 14 and month 1 postinfection (p.i.), and repeated monthly up to 6 months. The antibody responses were first detected as early as 14 days after infection. Hamsters that were infected with 100 MC and 50 MC showed higher antibody levels than those of 25 MC, during early infection until 1 month p.i. Then, the antibody levels were increased rapidly to a plateau at approximately month 2 p.i. and, subsequently, were relatively stable in all groups. The average antibody levels to egg and somatic, but not to ES antigens, were significantly higher in hamsters infected with 25 MC than those of 50 MC and 100 MC. These antibody responses, particularly to egg and ES antigens, were not correlated with worm burden or egg output. Overall, higher antibody responses were found in the order: ES, somatic and egg antigens. The significant lower antibody responses in chronic and heavy infections than those with mild infection may a result of immunosuppression.